In such prior Phipps U.S. Pat. No. 4,234,529, dated Nov. 18, 1980, there is disclosed air motors within a vacuum chamber into which foamable extrudate is extruded with the air motors controlling the speed of arcuate shaping rolls positioned downstream of the die.
As indicated in such prior art patent, ten internally mounted air motors are employed to drive the forming and shaping rolls, each being in the form of arcuate segmented drive rolls paired on each side of the arcuate orifice of the die within the chamber. Because of the harsh environmental conditions and crowded space, geared air motors were the devices thought to be most suitable. In such situation, only the air supply and exhaust needed to be ported into or out of the chamber. However, because of the harsh environment, control of speed, and especially torque with regard to the paired and sequentially paired downstream drive rolls were quite difficult and indeterminate. In addition to being driven at a precisely controlled speed and torque, the arcuate segmented rolls must be free to move up and down under controlled conditions, and also to open wide or to a maximum extent during any jam-ups or emergency conditions which might occur, further complicating the drive requirements.
In any event, because of the harsh conditions within the chamber, it was found difficult to control both torque and speed with air motors situated within the chamber. Moreover, if any corrections or repairs to existing drives located inside the chamber had to made, the chamber must then be opened. Before it could be opened, the entire system or production line must be brought to a halt. The production line would remain down as long as the chamber was open. Because of the loss of the established environmental conditions within the chamber and the long delays required to both shut down the line before the chamber could be opened an to restart the line once the chamber was closed, the down time of the system would be intolerable.